i'm also encountering the same error (20619,19901,13), i trird turning my anti-virus off but it still doesn't work.
Edited, Sep 1st 2010 11:10pm by Sleepymagi
Same error here. Looking into a solution.
Even though I disabled MSE, the error kept happening.
Restart your computer, whereupon your anti-virus (or MSE) should detect the Virus:DOS/SSR.gen.
There should be a drop down box to allow it, then you must allow it 'again' at the bottom of the window. IT should have a shield signifying needing admin rights.
Click allow, then open up the beta client updater (right click, run as admin) then let it do its thing.
After it is finished updating, it should take you to the login screen.